Optical module for connecting optical element and optical fiber

ABSTRACT

An optical module includes a mounting board, an optical element, an optical fiber having an optical axis, the optical fiber inserted in the mounting board to align the optical axis with the optical element, and a positioning mark provided to position the optical element on the mounting board. The mounting board has a groove provided in the middle of the mounting board and extending in a direction of the optical axis of the optical fiber, the groove enclosing the optical fiber when inserted. The groove has a vertical wall which is perpendicular to the direction of the optical axis and confronts a leading edge of the optical fiber when inserted. The positioning mark is located adjacent to an internal edge of the groove where the vertical wall is provided on the mounting board.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an optical module having an opticalelement, such as a laser-diode or a photo-diode, connected to an opticalfiber, and to a method of producing the optical module. Moreparticularly, the present invention relates to an optical module inwhich the optical element is supported on a mounting board and connectedto an optical fiber.

Recently, optical fiber transmission has made great progress. Theoptical fiber transmission has various advantages including transmissionof a large amount of data, a low level of loss, no cross talk, noradiation and the like. In order to develop an optical fibertransmission system for practical use, it is important that opticalparts, like the optical module, which constitute a part of the opticalfiber transmission system, have high reliability and good productivity.

(2) Description of the Related Art

FIGS. 1A, 1B and 1C show a conventional optical module. Referring toFIGS. 1A, 1B and 1C, an insulating layer 7 is formed on a mountingboard 1. The mounting board 1 is comprised of a silicon (Si) substrate,and the insulating layer 7 is a silicon dioxide (SiO₂) film. A metallayer 2 is formed on the insulating layer 7 as shown in FIG. 1A. AV-groove 4 is formed in the middle of the mounting board 1, the V-groove4 extending in a longitudinal direction of the mounting board 1. Anoptical fiber 8 is enclosed by the V-groove 4. The V-groove 4 extends ina direction of the optical axis of the optical fiber 8.

FIG. 1B is an enlarged view of a portion of the conventional opticalmodule where a laser-diode (LD) 3 and the optical fiber 8 are connected.As shown in FIG. 1B, a solder layer 9 is formed adjacent to an end ofthe V-groove 4, and the solder layer 9 is used to fix the laser-diode(LD) 3 to the mounting board 1. An electrode 5 is formed on theinsulating layer 7. The electrode 5 is made of gold (Au). The electrode5 is connected to and taken out from the solder layer 9, and theelectrode 5 extends from the end of the solder layer 9 in thelongitudinal direction of the mounting board 1.

The laser-diode (LD) 3 is positioned at a packaging location 10 on themounting board 1 to correctly perform the coupling of the laser-diode 3and the optical fiber 8 with respect to the direction of the opticalaxis of the optical fiber 8. The packaging location 10 is indicated by adotted line in FIG. 1B, and it surrounds the periphery of the solderlayer 9. A positioning mark 11 is provided on the mounting board 1 andattached to the electrode 5, and the positioning mark 11 is used toindicate the packaging location 10 for positioning the laser-diode 3 onthe mounting board 1 at a proper location. The positioning mark 11 has arectangular shape, and it is located at an opposite side to a side ofthe packaging location where the V-groove 4 is formed.

FIG. 1C is a cross-sectional view of the portion of the conventionaloptical module shown in FIG. 1B. As shown in FIG. 1C, the V-groove 4 hasa sloping wall 4a which confronts the leading edge of the optical fiber8. Since the sloping wall 4a of the V-groove 4 comes in contact with theoptical fiber 30 when the optical fiber 8 is placed in the V-groove 4 toapproach the laser-diode 3, the conventional optical module requires acertain amount of gap 12 between the laser-diode (LD) 3 and the opticalfiber 8. To reduce the gap 12 between the LD 3 and the optical fiber 8,it is necessary that the packaging position of the LD 3 on the mountingboard 1 is a position at which the LD 3 projects from the end of theV-groove 4 toward the V-groove 4, as shown in FIG. 1C.

If the positioning mark 11 is located adjacent to the V-groove 4, thepositioning mark 11 is concealed by the LD 3 and it cannot be used toposition the LD 3 on the mounting board 1 during the assembly.

The V-groove 4 is formed by etching of the silicon board 1, and theV-groove 4 has to include a sloping surface. This sloping surfacedepends on the characteristics of the silicon crystal structure of thesilicon board 1. The sloping surface of the V-groove 4 confronts theleading edge of the optical fiber 8 when inserted.

The above conventional optical module, shown in 1A, 1B and 1C, has aproblem, that is, it is difficult to perform the positioning of thelaser-diode 3 to the optical fiber 8 with high accuracy. To perform thepositioning of the laser-diode 3, one must observe the positioning mark11 which is located at the opposite side to the side of the packaginglocation 10 where the V-groove 4 is formed. In particular, it is verydifficult to achieve a required level of accuracy of the positioning ofthe laser-diode 3 by eliminating a misalignment or rotation of thelaser-diode 3 with respect to the direction of the optical axis of theoptical fiber 8. Since the positioning of the optical element on themounting board is difficult to perform, the conventional optical moduleproduced by using the above production method is not reliable, and theproductivity of the thus produced optical module is low.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved opticalmodule in which the above-mentioned problems are eliminated.

Another object of the present invention is to provide an optical modulewhich provides a high level of reliability and improves productivity.

Still another object of the present invention is to provide an opticalmodule which can be easily produced and allows the production of theoptical module with a high level of accuracy.

The above-mentioned objects of the present invention are achieved by anoptical module which includes: a mounting board; an optical elementsupported on the mounting board; an optical fiber having an opticalaxis, the optical fiber inserted in the mounting board to align theoptical axis with the optical element; and a positioning mark providedon the mounting board to position the optical element on the mountingboard, the mounting board having a groove provided in the middle of themounting board and extending in a direction of the optical axis of theoptical fiber, the groove enclosing the optical fiber when inserted, thegroove having a vertical wall which is perpendicular to the direction ofthe optical axis and confronts a leading edge of the optical fiber wheninserted, the positioning mark located adjacent to an internal edge ofthe groove where the vertical wall is provided on the mounting board.

The above-mentioned objects of the present invention are achieved by anoptical module which includes: a mounting board; an optical elementsupported on the mounting board; an optical fiber having an opticalaxis, the optical fiber inserted in the mounting board to align theoptical axis with the optical element; and a positioning mark providedon the mounting board to position the optical element on the mountingboard, the mounting board having a groove provided in the middle of themounting board and extending in a direction of the optical axis of theoptical fiber, the groove enclosing the optical fiber when inserted, thepositioning mark having a first projecting portion which inwardlyprojects over an internal edge of the groove and confronts a leadingedge of the optical fiber when inserted.

The above-mentioned objects of the present invention are achieved by anoptical module which includes: a mounting board; an optical elementsupported on the mounting board; an optical fiber having an opticalaxis, the optical fiber inserted in the mounting board to align theoptical axis with the optical element; and a retaining board provided onthe mounting board to retain the optical fiber, the mounting boardhaving a first groove provided in the middle of the mounting board andextending in a direction of the optical axis of the optical fiber, theretaining board having a second groove provided in the middle of theretaining board and extending in the direction of the optical axis ofthe optical fiber, the first groove and the second groove beingassociated to form an insertion hole through which the optical fiber isinserted.

The above-mentioned objects of the present invention are achieved by anoptical module which includes: a mounting board; at least one opticalelement supported on the mounting board; and at least one optical fiberhaving an optical axis, the optical fiber inserted in the mounting boardto align the optical axis with the optical element, the mounting boardhaving a groove extending in a direction of the optical axis of theoptical fiber, the groove enclosing the optical fiber when inserted, thegroove having a sloping surface which is perpendicular to the directionof the optical axis and confronts a leading edge of the optical fiberwhen inserted, the optical element being fixed to the sloping surface.

In the optical module of the present invention, the optical element canbe easily positioned on the mounting board by viewing the positioningmark adjacent to the internal edge of the groove. The present inventionthus makes it possible to easily produce the optical module, and theproduction of the optical module with a high level of accuracy.

Further, in the optical module of the present invention, the firstgroove of the mounting board and the second groove of the retainingboard are associated to form an insertion hole which facilitates theinsertion of the optical fiber. The present invention thus makes itpossible to easily and reliably perform the positioning of the opticalfiber.

Further, in the optical module of the present invention, the firstportions of the mounting board and the second portions of the retainingboard are connected with each other to position the mounting board andthe retaining board with respect to each other. The relative positionsof the mounting board and the retaining board on the optical module areeasily determined with a high level of accuracy. Thus, the positioningof the optical fiber on the optical module with a high level of accuracycan be easily performed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will bemore apparent from the following detailed description when read inconjunction with the accompanying drawings in which:

FIGS. 1A, 1B and 1C are diagrams of a conventional optical module;

FIGS. 2A and 2B are diagrams of an optical module in a first embodimentof the present invention;

FIGS. 3A through 3F are diagrams of a modification of the optical moduleshown in FIGS. 2A and 2B;

FIGS. 4A, 4B and 4C are diagrams of an optical module in a secondembodiment of the present invention;

FIGS. 5A and 5B are diagrams of a connecting portion of the opticalmodule shown in FIGS. 4A, 4B and 4C;

FIGS. 6A and 6B are diagrams of an optical module in a third embodimentof the present invention;

FIGS. 7A and 7B are diagrams of a modification of the optical moduleshown in FIGS. 6A and 6B;

FIGS. 8A and 8B are diagrams of an optical module in a fourth embodimentof the present invention;

FIGS. 9A and 9B are diagrams of an optical module in a fifth embodimentof the present invention;

FIG. 10 is an enlarged cross-sectional view of the optical module of thefifth embodiment;

FIGS. 11A through 11D are diagrams of a photo-diode array module towhich the fifth embodiment of the present invention is applied;

FIG. 12 is a diagram of a conventional photo-diode array module;

FIGS. 13A through 13G are diagrams for explaining a method of producingan optical module in a sixth embodiment of the present invention;

FIG. 14 is a top view of a modification of the optical module in thesixth embodiment;

FIGS. 15A and 15B are diagrams showing an optical module in a seventhembodiment of the present invention;

FIG. 16 is a diagram of an optical module in an eighth embodiment of thepresent invention;

FIGS. 17A, 17B and 17C are diagrams of an optical module in a ninthembodiment of the present invention;

FIGS. 18A through 18F are views of an optical module in a tenthembodiment of the present invention;

FIGS. 19A and 19B are cross-sectional views of an optical module in aneleventh embodiment of the present invention;

FIGS. 20A and 20B are diagrams for explaining a soldering process of theoptical module in the eleventh embodiment;

FIGS. 21A and 21B are diagrams of an optical module in a twelfthembodiment of the present invention;

FIGS. 22A, 22B and 22C are diagrams of a modification of the opticalmodule of the twelfth embodiment;

FIG. 23 is a diagram of a modification of the embodiment of FIGS. 22A,22B and 22C;

FIGS. 24A, 24B and 24C are diagrams of a modification of the embodimentof FIGS. 22A, 22B and 22C to improve the adhesion and stability of thesoldering;

FIGS. 25A, 25B and 25C are diagrams of an optical module in a thirteenthembodiment of the present invention;

FIGS. 26A through 26G are diagrams for explaining a method of producingthe optical module shown in FIGS. 25A, 25B and 25C;

FIGS. 27A through 27D are diagrams showing a connection of an opticalfiber by using an insert holder;

FIG. 28 is a diagram showing a connection of the insert holder and theoptical fiber by using a heat-shrinking tube;

FIGS. 29A and 29B are diagrams of an optical module in a fourteenthembodiment of the present invention; and

FIG. 30 is a diagram of an intermediate structure of the optical moduleusing an insert holder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of the preferred embodiments of thepresent invention with reference to the accompanying drawings.

FIGS. 2A and 2B show an optical module in a first embodiment of thepresent invention.

Referring to FIGS. 2A and 2B, an insulating layer 20 is formed on theentire surface of a mounting board 21. The mounting board 21 iscomprised of a silicon (Si) substrate, and the insulating layer 20 is asilicon dioxide (SiO₂) film. A V-groove 31 is formed in the middle ofthe mounting board 21, the V-groove 31 extending in a longitudinaldirection of the mounting board 21 from an external edge of the mountingboard 21 to an internal edge of the V-groove 31.

An optical fiber 30, shown in FIG. 2B, is inserted to the optical moduleand enclosed by the V-groove 31 in the middle of the mounting board 21.Thus, the V-groove 31 longitudinally extends in a direction of theoptical axis of the optical fiber 30 (which is the direction of theoptical axis of the optical fiber 30).

A solder layer 23 is formed on the mounting board 21 adjacent to theedge of the V-groove 31, and the solder layer 23 is used to fix alaser-diode (LD) 28 to the mounting board 21.

An electrode 22 is formed on the insulating layer 20 of the mountingboard 21. The electrode 22 is connected to the solder layer 23, andextends further from an end of the solder layer 23 in the longitudinaldirection of the mounting board 21 (the direction of the optical axis ofthe optical fiber 30).

In the first embodiment, a positioning mark 24, which is used toposition the laser-diode (LD) 28 on the mounting board 21, is formedadjacent to the edge of the V-groove 31. A transverse groove 29 whichcrosses the V-groove 31 on the mounting board 21 and extends in adirection perpendicular to the optical axis of the optical fiber 31, isformed on the mounting board 21. A vertical wall 29a is formed by thetransverse groove 29. The vertical wall 29a is located at the edge ofthe V-groove 31, and is perpendicular to the direction of the opticalaxis of the optical fiber 30. The vertical wall 29a is provided as astopper for positioning the optical fiber 30 when inserted, in thedirection of the optical axis of the optical fiber 30.

The groove 29 is formed by cutting of a cutting region 25 of themounting board 21, indicated by dotted lines in FIG. 2A. The verticalwall 29a, located at the end of the V-groove 31, is formed by formingthe groove 29 on the mounting board 21. Accordingly, the optical moduleof the first embodiment can place the end of the optical fiber 30 nearerto the laser-diode 28 on the mounting board 21 than the conventionaloptical module shown in FIGS. 1A through 1C.

More specifically, since the above first embodiment includes thevertical wall 29a, it is possible to make the gap 27 (FIG. 2B) betweenthe laser-diode (LD) 28 and the optical fiber 30, shown in FIG. 2B,smaller than the gap 12 (FIG. 1C) between the laser-diode (LD) 3 and theoptical fiber 8.

In the above first embodiment, even if the packaging location of thelaser-diode 28 is changed to a position slightly distant from the end ofthe V-groove 31, it is possible to keep the gap 27 smaller than the gap12 of the conventional optical module. Accordingly, the above firstembodiment makes it possible to provide the positioning mark 24 at theposition between the solder layer 23 and the end of the V-groove 31.

In the above first embodiment, when positioning the laser-diode 28 onthe mounting board 21, the laser-diode 28 is first placed at a packaginglocation 26 indicated by a dotted line in FIG. 2A, and the positioningof the laser-diode 28 can be performed by viewing the positioning mark24. Therefore, the above first embodiment can provide a wider tolerancezone of the positioning location at which the laser-diode 28 ispositioned, which is used to eliminate a misalignment or rotation of thelaser-diode 28 on the mounting board 21 with respect to the direction ofthe optical axis of the optical fiber 30. The first embodiment makes itpossible to perform more stably and easily the positioning of thelaser-diode 28 on the mounting board 21.

The positioning mark 24, shown in FIGS. 2A and 2B, is a set of dotswhich is aligned on the mounting board 21 along a transverse line at theedge of the V-groove 31. This positioning mark 24 facilitates thepositioning of the edge of the laser-diode 28 on the mounting board 21.A misalignment or rotation of the laser-diode 28 on the mounting board21 with respect to the direction of the optical axis of the opticalfiber 30 can more easily be eliminated.

As described above, the vertical wall 29a serves as the stopper forpositioning the optical fiber 30, when inserted, in the direction of theoptical axis of the optical fiber 30. If the leading edge of the opticalfiber 30, when inserted, comes into contact with the vertical wall 29a,the positioning of the optical fiber 30 can automatically be performed.

FIGS. 3A through 3F show a modification of the optical module shown inFIGS. 2A and 2B.

The vertical wall 29a of the optical module produced by using aproduction method shown in FIGS. 3A through 3F may be used alternativelyto that of the above first embodiment.

First, as shown in FIG. 3A, the positioning mark 24 is formed on theinsulating layer 20 of the mounting board 21 at the edge of the V-groove31. The insulating layer 20 for locations corresponding to small andlarge rectangular regions of the mounting board 21, indicated in FIG.3A, is not formed.

As shown in FIG. 3B, an etching using an aqueous solution of potassiumhydroxide (KOH) is performed to form the V-groove 31 in the middle ofthe mounting board 21 and a small rectangular groove 31a adjacent to theedge of the V-groove 31.

As shown in FIG. 3C, the electrode 22 is formed on the insulating layer20 of the mounting board 21, and the solder layer 23 is formed on theelectrode 22.

As indicated by dotted lines in FIG. 3D, the cutting region 25,including the internal edge of the V-groove 31 and the end of the groove31a (adjacent to the internal edge of the V-groove 31), is preset. Thecutting region 25 extends in a transverse direction perpendicular to thelongitudinal direction of the mounting board 21.

As shown in FIG. 3E, a cutting process of the cutting region 25 of themounting board 21 is performed so that a transversely extending verticalgroove 32 is formed on the mounting board 21.

Finally, as shown in FIG. 3F, the packaging of the optical fiber 30 onthe mounting board 21 is performed. A region 33 of the vertical groove32, indicated by shaded lines in FIG. 3F, serves as the stopper forpositioning the optical fiber 30 when inserted, in the direction of theoptical axis of the optical fiber 30.

The region 33 of the stopper, shown in FIG. 3F, is greater in area thanthe vertical wall 29a of the stopper shown in FIG. 2B. The groove 31ashown in FIG. 3B has a width less than the width of the V-groove 31. Forthis reason, the stopper function of the region 33 of this embodiment inFIGS. 3A through 3F to position the optical fiber 30 on the mountingboard 21 is more reliable and/or safer than the stopper function of thevertical wall 29a of the above first embodiment in FIGS. 2A and 2B.

In the embodiment shown in FIG. 3F, the groove of the optical moduleincludes a first portion (the V-groove 31) having a first width and asecond portion (the groove 31a) having a second width less than thefirst width, the first portion 31 enclosing the optical fiber 30therein, the second portion 31a located adjacent to the positioning mark24, and the vertical wall 29a located between the first portion 31 andthe second portion 31a.

FIGS. 4A, 4B and 4C and FIGS. 5A and 5B show an optical module in asecond embodiment of the present invention and a method of producing theoptical module of the second embodiment. The optical module of thesecond embodiment includes a positioning mark 24A and stoppers 34 whichare different from those of the above-described first embodiment.

As shown in FIG. 4A, an insulating layer 20A (the SiO₂ film) is formedon a mounting board 21A (the silicon substrate). A positioning mark 24Ais formed on the insulating layer 20A of the mounting board 21A at aposition as indicated in FIG. 4A.

As shown in FIG. 4B, an etching of the mounting board 21A using anaqueous solution of potassium hydroxide (KOH) is performed to form aV-groove 31A in the middle of the mounting board 21A. By this etching,the positioning mark 24A and the stoppers 34 on the insulating layer 20Aare formed such that the positioning mark 24A projects from the edge ofthe V-groove 31A in the longitudinal direction of the mounting board21A, and the stoppers 34 project toward the inside of the V-groove 31ain the transverse direction of the mounting board 21A.

As shown in FIG. 4C, an electrode 22A and a solder layer 23A are formedon the insulating layer 20A of the mounting board 21A.

When the laser-diode 28 is packaged on the mounting board 21A, thepositioning of the laser-diode 28 on the mounting board 21A can beperformed by viewing the positioning mark 24A. As shown in FIGS. 5A and5B, the laser-diode 28 is partially overlapped on the positioning mark24A, and the laser-diode 28 located at a packaging location 26A, afterthe positioning is performed, projects from the edge of the V-groove 31Atoward the inside of the V-groove 31A. The packaging location 26A of thelaser-diode 28 is indicated by a dotted line in FIG. 5B.

The optical module of the second embodiment does not include verticalwall like the vertical wall 29a of the first embodiment. However, thesloping wall of the V-groove 31A of the second embodiment does notinterfere with the leading edge of the optical fiber. Since thepositioning mark 24A projects from the edge of the V-groove 31A and thestoppers 34 project toward the inside of the V-groove 31a, the gap 27Abetween the laser-diode 28 and the optical fiber 30 in the secondembodiment can be reduced to an appropriate length.

When the leading edge of the optical fiber 30, after inserted, touchesthe two opposing stoppers 34 as shown in FIG. 5B, the optical fiber 30is automatically positioned at a packaging location 30a. The packaginglocation 30a of the optical fiber 30 is indicated by a dotted line inFIG. 5B.

The method of producing the optical module of the second embodimentshown in FIGS. 4A through 4C does not require the cutting process of thefirst embodiment to form the transverse groove 29. The stoppers 34 andthe V-groove 31A can be formed at the same time by the V-groove formingprocess of the second embodiment. Thus, the production method of thesecond embodiment can be performed more easily than the productionmethod of the first embodiment.

FIGS. 6A and 6B show an optical module in a third embodiment of thepresent invention. The optical module of the third embodiment provides aconstruction in which the optical fiber can automatically be positionedon the mounting board with the required level of accuracy.

As shown in FIG. 6A, an optical fiber stopper 36 and a laser-diodepositioning mark (not shown) which are similar to those of the first andsecond embodiments are formed on a mounting board 35 (the siliconsubstrate). Similarly to the first and second embodiments, a V-groove 42for enclosing the optical fiber 30 is formed in the middle of themounting board 35. The V-groove 42 extends in the longitudinal directionof the mounting board 35.

Further, in the third embodiment, fitting grooves 37, each of whichextends in a direction parallel to the longitudinal direction of themounting board 35, are formed on the mounting board 35 at both sides ofthe V-groove 42. Cylindrical parts 40 (such as optical fibers) areinserted into the fitting grooves 37.

Further, in the third embodiment, a retaining board 38 (the siliconsubstrate) is provided to retain the cylindrical parts on the mountingboard 35. A V-groove 42A corresponding to the V-groove 42 and fittinggrooves 39 corresponding to the fitting grooves 37 are formed on theretaining board 38. The retaining board 38 is placed on the mountingboard 35. The mounting board 35, the fitting grooves 37 and theretaining board 38 are fixed together via the cylindrical parts 40 byusing an adhesive agent.

As shown in FIG. 6B, an insertion hole 41 to which the optical fiber 30is inserted is formed by the V-groove 42 and the V-groove 42A.

The insertion hole 41 has an inside diameter slightly greater than anoutside diameter of the optical fiber 30. For example, when the outsidediameter of the optical fiber 30 is 125 μm, the inside diameter of theinsertion hole 41 is 126 μm.

In the third embodiment, the optical fiber 30 is inserted into theinsertion hole 41, and when the leading edge of the optical fiber 30touches the stopper 36, the positioning of the optical fiber 30 on themounting board 35 is automatically performed. The optical coupling ofthe optical fiber 30 and the laser-diode 28 is achieved with therequired level of accuracy.

Since it is not necessary to handle many parts at the same time,performing the method of producing the optical module in theabove-described third embodiment is very simple. The positioning of theoptical fiber 30 on the mounting board 35 is automatically performed byinserting the optical fiber 30 and bringing it into contact with thestopper 36. The method of producing the optical module in the thirdembodiment is advantageous to realize volume production, low price andhigh reliability of the optical module.

In the above third embodiment, as shown in FIGS. 6A and 6B, two sets ofthe fitting grooves 37 and the fitting grooves 39 are provided. However,the present invention is not limited to this embodiment, and one fittinggroove 37 and one fitting groove 39 may be provided, or three or moresets of the fitting grooves 37 and the fitting grooves 39 may beprovided.

FIGS. 7A and 7B show a modification of the third embodiment.

As shown in FIG. 7A, instead of the retaining board 38 shown in FIGS. 6Aand 6B, a retaining board 38A is provided in this embodiment. Theretaining board 38A includes two fitting portions 39A corresponding tothe fitting grooves 37 of the mounting board 35. The retaining board 38Aincludes no V-groove 42A corresponding to the V-groove 42 of themounting board 35. The fitting portions 39A are fitted into the fittinggrooves 37 of the mounting board 35, and the retaining board 38A and themounting board 35 are fixed together by using an adhesive agent.

As shown in FIG. 7B, an insertion hole 41A to which the optical fiber 30is inserted is formed by the V-groove 42 of the mounting board 35.

The insertion hole 41A has an inside diameter slightly greater than anoutside diameter of the optical fiber 30. For example, when the outsidediameter of the optical fiber 30 is 125 μm, the inside diameter of theinsertion hole 41A is 126 μm.

In the present embodiment, shown in FIG. 7B, the top of the opticalfiber 30 when inserted touches the flat bottom surface of the retainingboard 38A. Since it is not necessary to handle many parts at the sametime, performing the method of producing the optical module in theabove-described embodiment is very simple. The positioning of theoptical fiber 30 on the mounting board 35 is automatically performed byinserting the optical fiber 30 and bringing it into contact with thestopper 36. The method of producing the optical module in the presentembodiment is advantageous to provide volume production, low price andhigh reliability of the optical module.

FIGS. 8A and 8B show an optical module in a fourth embodiment of thepresent invention. Similar to the above third embodiment, the opticalmodule of the fourth embodiment has a construction in which the opticalfiber can automatically be positioned on the mounting board with arequired level of accuracy.

Referring to FIGS. 8A and 8B, the optical fiber stopper 36 and thelaser-diode positioning mark (not shown) which are similar to those ofthe first and second embodiments are formed on a mounting board 35A (thesilicon substrate). Similar to the third embodiment, the V-groove 42 forenclosing the optical fiber 30 is formed in the middle of the mountingboard 35A. The V-groove 42 extends in the longitudinal direction of themounting board 35A.

In the fourth embodiment, a glass capillary 43 is placed into theV-groove 42 on the mounting board 35A, and the glass capillary 43 andthe mounting board 35A are fixed together by using an adhesive agent.

As shown in FIG. 8B, the glass capillary 43 has an insertion hole 41B towhich the optical fiber 30 is inserted. The insertion hole 41B has aninside diameter slightly greater than the outside diameter of theoptical fiber 30. The glass capillary 43 is produced with its outsideand inside diameters having dimensions within a tolerance of ±1 μm. Forexample, when the outside diameter of the optical fiber 30 is 125 μm,the inside diameter of the insertion hole 41B of the glass capillary 43is 126 μm.

In the fourth embodiment, the optical fiber 30 is inserted into theinsertion hole 41B, and, when the leading edge of the optical fiber 30touches the stopper 36, the positioning of the optical fiber 30 on themounting board 35A is automatically performed. The method of producingthe optical module in the present embodiment is advantageous to realizevolume production, low price and high reliability of the optical module.

Further, in the fourth embodiment, a retaining board having a V-groovewhich is the same as the retaining board 38 of the third embodimentshown in FIGS. 6A and 6B may be provided. This retaining board and themounting board 35A are fixed together via the glass capillary 43 byusing an adhesive agent.

FIGS. 9A and 9B show an optical module in a fifth embodiment of thepresent invention. The optical module of the fifth embodiment provides aconstruction having a photo-diode as the optical element, which improvesthe coupling of the optical fiber and the photo-diode.

Referring to FIGS. 9A and 9B, a V-groove 54 for enclosing the opticalfiber 30 is formed in the middle of a mounting board 51 (the siliconsubstrate). A recessed portion 54A for enclosing a photo-diode (PD) 55is formed on the mounting board 51. The V-groove 54 and the recessedportion 54A are formed by etching of the mounting board 51 using theaqueous solution of potassium hydroxide (KOH). The recessed portion 54Ahas a sloping surface 53 which confronts the leading edge of the opticalfiber 30 when inserted. This sloping surface 53 (which is identified as(111) plane of the silicon crystal structure) depends on thecharacteristics of the silicon crystal structure of the siliconsubstrate, and is at an angle of 54.74° to the horizontal surface (whichis identified as (100) plane of the silicon crystal structure) of thesilicon substrate.

The photo-diode (PD) 55 is mounted on the sloping surface 53 of themounting board 51. Hereinafter, the sloping surface 53 is called the PDmounting surface. An electrode 52 is formed on an insulating layer (theSiO₂ film) of the mounting board 51, and extends from the PD mountingsurface 53 in the longitudinal direction of the mounting board 51.

FIG. 10 is an enlarged view of the PD mounting surface 53 of themounting board 51 shown in FIGS. 9A and 9B. As shown in FIG. 10, a lightreceiving surface 55a is formed at a portion of the bottom surface ofthe photo-diode 55, and a focusing lens 56 is provided at a portion ofthe top surface of the photo-diode 55. The focusing lens 56 functions todirect an incident light ray from the optical fiber 30 to the lightreceiving surface 55a of the photo-diode 55. Since the light receivingsurface 55a is slanting to the direction of the optical axis of theoptical fiber 30, the position of the focusing lens 56 downwardlydeviates from the center of the light receiving surface 55a. There is apreset offset between the center of the light receiving surface 55a andthe center of the focusing lens 56, as shown in FIG. 10. For example,the above offset is preset to 30 μm when the diameter of the lightreceiving surface 55a is 40 μm, the diameter of the focusing lens 56 is80 μm, and the thickness "t" of the photo-diode 55 is 150 μm. For thisreason, it is possible that the focusing lens 56 of the fifth embodimentcorrectly directs the light ray from the optical fiber 30 to the centerof the light receiving surface 55a.

The photo-diode 55 is fixed to the PD mounting surface 53 of themounting board 51 by soldering.

As shown in FIG. 9B, the optical fiber 30 is placed on the mountingboard 51 and positioned thereon, and a retaining board 156 (the siliconsubstrate) is placed onto the mounting board 51 so that the opticalfiber 30 is retained by the retaining board 156.

In the fifth embodiment, a photo-diode positioning mark (not shown)which is similar to the positioning mark 24 of the first embodiment isformed on the mounting board 51 along the edge of the recessed portion54A. The positioning of the photo-diode 55 on the mounting board 51 canbe performed while viewing this positioning mark. This makes itunnecessary to perform the adjusting of the optical axis of the opticalfiber 30 in relation to the position of the photo-diode 55.

In the above fifth embodiment, it is not necessary to handle many partsat the same time, and the method of assembling the optical module in thepresent embodiment is very simple. The method of producing the opticalmodule in the present embodiment is advantageous for volume production,low price and high reliability of the optical module.

The photo-diode 55 in the present embodiment is a type having the lightreceiving surface 55a on the bottom side of the photo-diode 55. However,a photo-diode of a type having the light receiving surface 55a on thefront side may be used instead for the present embodiment.

FIGS. 11A through 11D show a photo-diode array module to which the fifthembodiment of the present invention is applied.

As shown in FIG. 11A, a plurality of V-grooves 54B and a recessedportion 54C are formed on a mounting board 57 (the silicon substrate) byetching. Sloping surfaces of the V-grooves 54B and a sloping surface 54Dof the recessed portion 54C are formed by (111) plane of the siliconcrystal structure which depend on the characteristics of the crystalstructure of the silicon substrate. The top surface of the mountingboard 57 is formed by (100) plane of the silicon crystal structure.

As shown in FIG. 11B, a plurality of electrodes 58 (Au) are formed onthe mounting board 57. The electrodes 58 extend from the sloping surface54D (the array mounting surface) of the recessed portion 54C. Further, asolder layer 59 is formed on the array mounting surface 54D.

As shown in FIG. 11C, a photo-diode array 60, including a plurality ofphoto-diodes of the type having the light receiving surface on thebottom side, is placed on the solder layer 59. The photo-diode array 60is fixed to the solder layer 59 on the array mounting surface 54D bysoldering.

As shown in FIG. 11D, an optical fiber array 30A including a pluralityof optical fibers is placed on the V-grooves 54B. A retaining board 61(the silicon substrate) is placed on the optical fibers of the opticalfiber array 30A, and the optical fibers are retained by the retainingboard 61.

FIG. 12 shows a conventional photo-diode array module which is relatedto the above fifth embodiment. Referring to FIG. 12, a photo-diode array46 including a plurality of photo-diodes of the type having the lightreceiving surface on the bottom side, is coupled to an optical fiberarray 50 including a plurality of optical fibers. The photo-diode array46 is packaged on a carrier 47, and the carrier 47 with the photo-diodearray 46 is supported on a metal stem 45. The optical fiber array 50 hasa ferrule 48 at its leading edge, and the optical fiber array 50 issupported on a metal frame 49. The photo-diode array 46 is fixed to theoptical fiber array 50 after the adjusting of the optical axis of theoptical fiber array 50 is performed.

In the above conventional photo-diode array module, it is necessary tohandle many parts at the same time, and the method of assembling thisconventional module is complicated. The method of producing the aboveconventional module is not appropriate for volume production, and thereliability of the conventional module is poor.

However, in the photo-diode array module of the above fifth embodiment,it is not necessary to handle many parts at the same time, and themethod of assembling the optical module in the present embodiment issimple. The method of producing the optical module in the presentembodiment is advantageous for volume production, low price and highreliability of the optical module.

FIGS. 13A through 13G show an optical module in a sixth embodiment ofthe present invention. It is desirable that the optical modules of thefirst through fifth embodiments described above are enclosed by a metalpackage (metal case).

In the sixth embodiment which will be described below, the opticalmodule of the first embodiment is enclosed by a metal case. Also, theoptical modules of the second through fifth embodiments may be enclosedby a metal case in a similar manner.

Referring to FIGS. 13A and 13B, the optical element 28 (the laser-diodein the first embodiment) is mounted on the mounting board 21 having theV-groove. The mounting board 21 with the optical element 28 is joined toa base 73 of a metal case 63 by using a solder sheet 75. The metal case63 is made of, for example, aluminum (Al). The solder sheet 75 isinserted between the mounting board 21 and the base 73. During solderingof the solder sheet 75, the entire metal case 63 is heated while themounting board 21 is loaded against the base 73 by a weight.

The metal case 63 includes an insertion hole 63a at one side and aninsertion hole 63b at the opposite side. The optical fiber 30 is passedthrough the insertion hole 63a, and a signal-line drawing member 78 ispassed through the insertion hole 63b.

Referring to FIGS. 13C and 13G, an optical fiber cut-piece 64 isinserted in the metal case 63 through the insertion hole 63a. Theoptical fiber cut-piece 64 in the present embodiment is a piece ofoptical fiber having a small length with no protection coat. The opticalfiber cut-piece 64 is retained by the retaining board 69 having theV-groove.

The metal case 63 in the present embodiment is made of Kovar. Kovar is aFe--Co--Ni alloy including 54% iron (Fe), 17% cobalt (Co), and 29%nickel (Ni).

Referring to FIG. 13D, the insertion hole 63a of the metal case 63 isfilled with a solder 65, and the optical fiber cut-piece 64 is fixed tothe metal case 63 by soldering.

Referring to FIG. 13E, after a wire bonding for electrical connection isperformed, a lid 66 (the material of which is the same as the materialof the metal case 63) is placed on the metal case 63, and the inside ofthe metal case 63 is hermetically sealed by the lid 66.

The optical module shown in FIG. 13E may be a final state of the opticalmodule. However, when taking into account the following productionprocesses, the optical module of FIG. 13E may be called an intermediatestructure.

Referring to FIG. 13F, the optical fiber 30 with a connector 72 isattached to the intermediate structure. An insert holder 70 is attachedto the metal case 63, so that the optical fiber cut-piece 64 and theoptical fiber 30 with the connector 72 (provided in a guide groove 70A)are connected to each other by a glass capillary 71 (provided within theinsert holder 70).

The optical fiber 30 in the previous embodiments is directly attached tothe optical module. However, it is possible to use instead the finalstructure of the optical module shown in FIG. 13F.

When the method of producing the optical module in the sixth embodimentshown in FIGS. 13A through 13F is used, the adjustment of the opticalaxis of the optical fiber 30 to the optical element 28 is automaticallyperformed when the optical fiber cut-piece 64 is fixed to the V-grooveof the mounting board 21. It is no longer necessary to monitor the stateof the coupling between the optical fiber and the optical element asrequired by the conventional production method.

In the above sixth embodiment, the use of the optical fiber cut-piece 64makes the handling of the optical module easier than that when theoptical fiber 30 is solely used, and the productivity of the opticalmodule is improved. Further, in the above sixth embodiment, since theoptical element 28 and the optical fiber 64 are packaged on the samemounting board 21, the number of the parts constituting the opticalmodule is reduced. Accordingly, the optical module shown in FIGS. 13Athrough 13G is suitable for a method of production the optical moduleusing automatic machines. The method of producing the optical module inthe sixth embodiment is advantageous to provide volume production, lowprice and high reliability of the optical module.

In the case in which the optical element 28 is a laser-diode (LD), theoptical module when operated tends to generate a certain degree of heatenergy. The mounting board 21 on which the laser diode 28 is supportedis fixed to the base 73 of the metal case 63. In the above sixthembodiment, a relatively large area where the laser diode 28 and thebase 73 are in contact can be produced, and a heat passage large enoughto discharge the heat generated by the optical module can be formed. Bymaking the thickness of the base 73 of the metal case 63 small, it ispossible to provide a small-thickness, small-size optical module.

Suppose that the optical modules of the third and fourth embodiments areenclosed by the metal case 63. In such a case, also, the positioning ofthe optical fiber can easily be performed by simply inserting theoptical fiber cut-piece 64 into the insertion hole 63a. The method ofproducing the optical module in the sixth embodiment is advantageous toprovide good productivity of the optical modules.

FIG. 14 shows a modification of the optical module in the sixthembodiment. As shown in FIG. 14, it is desirable to make a lateral widthof the base 73 of the metal case 63 equal to a lateral width of themounting board 21, in order to facilitate the positioning of themounting board 21 on the base 73 of the metal case 63. In thismodification, if the mounting board 21 is positioned on the base 73 suchthat the side surfaces of the mounting board 21 and the side surfaces ofthe base 73 are flush with each other, the insertion hole 63a of themetal case 63 and the V-groove of the mounting board 21 accurately alignwith each other. Therefore, by this modification, it is possible toprovide accurate positioning of the V-groove of the mounting board 21 tothe insertion hole 63a of the metal case 63 without using a specialpositioning jig.

As described above, during the soldering of the solder sheet 75, theentire metal case 63 is heated while the mounting board 21 is loadedagainst the base 73 by the weight. By this soldering, an oxide film onthe surface of the solder sheet 75 may be formed. If the oxide film isformed there, it is difficult to obtain an adequate level of theadhesion between the mounting board 21 and the base 73 by the soldering.To avoid the formation of the oxide film, it is desirable to vibrate orscrub either the mounting board 21 or the metal case 63 while the metalcase 63 is heated. Hereinafter, this process is called the scrubbingprocess.

FIGS. 15A and 15B show an optical module in a seventh embodiment of thepresent invention. The optical module in the seventh embodiment makes itpossible to obtain an adequate level of the adhesion without performingthe above-mentioned scrubbing process.

As shown in FIG. 15A, the optical module in the present embodiment useseither a mounting board 76A (the silicon substrate) having a bottom onwhich an array of projections 77A is formed, or a mounting board (thesilicon substrate) 76B having a bottom on which an array of recesses 77Bare formed. The bottom of the mounting board 76A or the mounting board76B is fixed to the base 73 of the metal case 63 via the solder sheet75. The projections 77A or the recesses 77B can be formed on the siliconsubstrate by performing the etching using the aqueous solution ofpotassium hydroxide (KOH).

As shown in FIG. 15B, the mounting board 76A or the mounting board 76Bdescribed above is placed on the base 73 of the metal case 63 via thesolder sheet 75. The entire metal case 63 is heated while the mountingboard 21 is loaded against the base 73 by the weight, to perform thesoldering of the solder sheet 75. During the above soldering, theprojections 77A on the bottom of the mounting board 76A or the recesses77B on the bottom of the mounting board 76B prevents the formation ofthe oxide film on the surface of the solder sheet 75. Therefore, it ispossible to obtain an adequate level of the adhesion between themounting board and the base 73 of the metal case 63 by the soldering. Itis no longer necessary to perform the scrubbing process, and the methodof producing the optical module can be made simple by the presentembodiment.

Alternatively, it is possible that the above projections 77A or theabove recesses 77B be formed on the base 73 of the metal sheet 63. Inshort, in the above seventh embodiment, the above projections 77A or theabove recesses 77B may be formed on at least one of the bottom of themounting board and the top of the base 73.

Since the optical fiber cut-piece 64 having no protection coat is usedby the above sixth embodiment, the strength of this optical fiberagainst damage may not be sufficient. If the optical fiber cut-piece 64is subjected to a bending stress before the intermediate structure shownin FIG. 13E is produced, the optical fiber cut-piece 64 is likely to bedamaged or cut away. This problem can be eliminated if careful attentionis paid to the handling of the optical fiber cut-piece 64 during theproduction.

FIG. 16 shows an optical module in an eighth embodiment of the presentinvention. The optical module in the eighth embodiment makes theabove-mentioned handling of the optical fiber cut-piece 64 during theproduction easier.

Referring to FIG. 16, the optical fiber cut-piece 64 has a protectioncoat 80 located around a portion where the optical fiber cut-piece 64and the insertion hole 63a of the metal case 63 join. Further, theoptical fiber cut-piece 64 has a metal plating (not shown in FIG. 16)located at portions where the protection coat 80 is located and wherethe optical fiber cut-piece 64 and the V-groove of the mounting board 21join. The protection coat 80 in this embodiment is made of any ofcarbon, polyimide, urethane, silicon, acrylic polymer, etc. Theprotection coat 80 is about 1 μm thick. The metal plating in thisembodiment is deposited on the optical fiber cut-piece 64 by any ofnickel (Ni) plating, gold (Au) electrolytic plating, and Ni--Cr/Cusputtering. The metal plating is about 1 μm thick.

In the above eighth embodiment, the optical fiber cut-piece 64 has themetal plating at the portion where the cut-piece 64 is joined with theV-groove of the mounting board 21 with no protection coat located atthis portion. The optical module of the present embodiment can providean adequate level of accuracy of the optical fiber packaging for theportion where the optical fiber cut-piece 64 and the V-groove join.Further, in the above eighth embodiment, the optical fiber cut-piece 64has the protection coat 80 around the portion where the insertion hole63a and the optical fiber cut-piece 64 join. The strength of such aportion of the optical fiber cut-piece 64 against the bending stress canremarkably be increased by the protection coat 80. Therefore, theoptical module of this embodiment can make the above handling of theoptical fiber cut-piece 64 during the production easier, and improvesthe productivity of the optical module.

As described above, in the optical module of the sixth embodiment asshown in FIGS. 13A through 13G and 14, if the mounting board 21 ispositioned on the base 73 such that the side surfaces of the mountingboard 21 and the side surfaces of the base 73 are flush with each other,the insertion hole 63a of the metal case 63 and the V-groove of themounting board 21 accurately accord with each other on a horizontalplane. However, as a practical problem, if a lower level of accuracy ofthe positioning of the optical axis of the optical fiber to the V-grooveof the mounting board 21 can be allowed, the ease of production of theoptical module will be further increased.

FIGS. 17A, 17B and 17C show an optical module in a ninth embodiment ofthe present invention. The optical module in this embodiment allows alower level of accuracy for positioning of the optical axis of theoptical fiber to the V-groove of the mounting board to be performed.

As shown in FIG. 17A, a front edge of a V-groove 82 of a mounting board81 (the silicon substrate) is tapered. This front edge of the V-groove82 is located at a side of the mounting board 81 confronting the leadingedge of the optical fiber cut-piece 64 when it is inserted through theinsertion hole 63a of the metal case 63. A tapered portion 82A at thefront edge of the V-groove 82 is formed such that the tapered portion82A has an arbitrary taper angle. This tapered portion 82A includessloping surfaces ((331) plane of the silicon crystal structure) andsloping surfaces ((331) plane of the silicon crystal structure), asshown in FIG. 17A. The sloping surface (the (331) plane) and the slopingsurfaces (the (331) plane) depend on the characteristics of the siliconcrystal structure of the silicon substrate. Since the optical module ofthe present embodiment includes the tapered portion 82A of the V-groove82 which facilitates the insertion of the optical fiber cut-piece 64, alower level of accuracy for positioning of the optical axis of theoptical fiber to the V-groove of the mounting board is allowed.

However, the sloping surfaces (the (331) plane) of the tapered portion82A have a taper angle of 153.43° as shown in FIG. 17A, and this taperangle is relatively great. For this reason, the leading edge of theoptical fiber cut-piece 64 when inserted may hit the sloping surfaces(the (331) plane), causing a problem on the production of the opticalmodule.

In order to avoid the above-mentioned problem, it is desirable to use atapered portion 83 of the V-groove 82 shown in FIGS. 17B and 17C. Thesloping surfaces (331) of the tapered portion 83 have a taper angle of53.14°, and this taper angle is relatively small. For this reason, theleading edge of the optical fiber cut-piece 64 can smoothly be insertedin the V-groove 82 even if the leading edge touches the tapered portion83.

In the present embodiment, the formation of the sloping surfaces (the(331) plane) of the tapered portion is avoided by making the taperedportion having a taper angle of 53.14° or below.

In the optical module of the sixth embodiment shown in FIGS. 13A through14, the insertion hole 63a of the metal case 63 is filled with thesolder 65, for sealing the metal case 63, after the optical fibercut-piece 64 is passed through the insertion hole 63a. In order toperform the soldering suitably, the diameter of the insertion hole 63ashould not be made too large.

Further, in the optical module of the sixth embodiment, the mountingboard 21 is packaged within the metal case 63. In order to prevent theoptical fiber cut-piece 64 from interfering with the mounting board 21when the optical fiber cut-piece 64 is inserted in the V-groove 82, itis necessary to slightly raise the optical fiber cut-piece 64 above themounting board 21 when inserted. For this reason, a range of theinsertion hole 63a in which the optical fiber cut-piece 64 can smoothlybe passed is somewhat narrow, and a high level of accuracy for thepositioning is needed.

However, as a practical problem, if a lower level of accuracy forpositioning of the optical axis of the optical fiber to the V-groove ofthe mounting board 21 can be allowed, the ease of production of theoptical module will be further increased.

FIGS. 18A through 18F show an optical module in a tenth embodiment ofthe present invention. The optical module in the tenth embodiment allowsa lower level of accuracy for positioning of the optical axis of theoptical fiber to the V-groove of the mounting board with respect to avertical plane to be performed.

FIG. 18A is a top view of the optical module of the tenth embodiment,FIG. 18B is a cross-sectional view of this optical module (when theoptical fiber is inserted). taken along the optical axis of the opticalfiber, FIG. 18D is a cross-sectional view of this optical module (whenthe optical fiber is fixed) taken along the optical axis of the opticalfiber, FIGS. 18C and 18E are side views of this optical module where theinsertion hole 63a is provided (corresponding to FIGS. 18B and 18Drespectively), and FIG. 18F is an enlarged view of the optical module inFIG. 18E.

As shown in FIGS. 18A through 18F, in the optical module of the tenthembodiment, the center of the optical fiber cut-piece 64 when it isplaced on the V-groove 31 of the mounting board 21 deviates from thecenter of the insertion hole 63a of the metal case 63. The insertionhole 63a of the metal case 63 is formed such that the center of theoptical fiber cut-piece 64 when placed on the V-groove 31 of themounting board 21 is located below the center of the insertion hole 63a.When the optical fiber cut-piece 64 is fixed to the mounting board 21 bythe soldering, the optical fiber cut-piece 64 in the fixed state doesnot touch the inside periphery of the insertion hole 63a, as shown.

In the above tenth embodiment, when the optical fiber cut-piece 64 isinserted, the center of the optical fiber cut-piece 64 is slightlyraised above the mounting board 21. Thus, at this time, the center ofthe optical fiber cut-piece 64 and the center of the insertion hole 63acan be aligned with each other. After the optical fiber cut-piece 64 isfixed to the mounting board 21, the center of the optical fibercut-piece 64 is located below the center of the insertion hole 63a.However, the optical fiber cut-piece 64 when fixed does not touch theinside periphery of the insertion hole 63a.

Accordingly, since the insertion of the optical fiber cut-piece 64 tothe mounting board 21 at a height of the center of the insertion hole63a can be smoothly performed, a lower level of accuracy for positioningof the optical axis to the V-groove 31 of the mounting board 21 withrespect to a vertical plane is allowed by the above tenth embodiment.

In the optical module of the sixth embodiment shown in FIGS. 13A through14, it is desirable to monitor a soldering condition after the opticalfiber cut-piece 64 is fixed to the metal case 63 by soldering of thesolder in the insertion hole 63a of the metal case 63. This monitoringof the soldering condition is performed by viewing the insertion hole63a from the outside of the metal case 63. However, if the monitoring ofthe soldering condition can be performed by viewing the insertion hole63a from the inside of the metal case 63, it is advantageous to improvethe yield of the thus produced optical modules.

FIGS. 19A and 19B show an optical module in an eleventh embodiment ofthe present invention. The optical module in the eleventh embodimentallows the monitoring of the soldering condition to be performed byviewing the insertion hole 63a from the inside of the metal case 63.

As shown in FIG. 19A, the retaining board 69 in the present embodimentis located apart from an inside wall of the metal case 63 where theinsertion hole 63a is provided. When the soldering is performed, thesolder from the insertion hole 63a is spread over a space between theretaining board 69 and the inside wall of the metal case 63, asindicated by an arrow "A" in FIG. 19A. Thus, it is possible to monitorthe soldering condition by viewing the insertion hole 63a from theinside of the metal case 63.

As shown in FIG. 19B, both the retaining board 69 and the mounting board21 in the present embodiment are located apart from the inside wall ofthe metal case 63 where the insertion hole 63a is provided. Also, in thepresent embodiment, when the soldering is performed, the solder from theinsertion hole 63a is spread over the space between the mounting board21 and the inside wall of the metal case 63, as indicated by an arrow inFIG. 19B. Thus, it is possible to monitor the soldering condition byviewing the insertion hole 63a from the inside of the metal case 63.

In the eleventh embodiment as shown in FIGS. 19A and 19B, it isnecessary that both the retaining board 69 and the mounting board 21include a V-groove which is long enough to position the optical fibercut-piece 64 on the mounting board 21.

In the above eleventh embodiment, since the soldering condition can bemonitored by viewing the insertion hole 63a from the inside of the metalcase 63, it is possible to improve the yield of the produced opticalmodules.

FIGS. 20A and 20B show a soldering process of the optical module in theeleventh embodiment in FIGS. 19A and 19B. A soldering process shown inFIG. 13D is the same as the soldering process shown in FIGS. 20A and20B.

As shown in FIG. 20A, the signal-line drawing member 78 is inserted in ahot plate 85, and the metal case 73 is vertically supported on the hotplate 85. A solder preform 86, which is a solder of a hollow,cylindrical form, is provided at a predetermined portion of the opticalfiber cut-piece 64, and the optical fiber cut-piece 64 is placed on aside wall of the metal case 63. In FIGS. 20A and 20B, the side wall ofthe metal case 63 is horizontally provided. The metal case 63 is heatedby using the hot plate 85 when the optical module is in the conditionshown in FIG. 20A, so that the solder preform 86 is melted by the heat.

As shown in FIG. 20B, since the solder preform 86 is melted by the abovesoldering, the solder is spread out at the external portions of theinsertion hole 63a of the metal case 63, and the solder finallysolidifies, as indicated by an arrow "B" in FIG. 20B.

In the optical module of the eleventh embodiment shown in FIGS. 20A and20B, the flatness of the external side wall of the metal case 63 becomespoor due to the spread-out solder. If the flatness of the external sidewall of the metal case 63 is poor, the optical module having such ametal case may experience a difficulty in attaching the insert holder 70to the metal case 63 as shown in FIG. 13F.

FIGS. 21A and 21B show an optical module in a twelfth embodiment of thepresent invention. The optical module of the twelfth embodimenteliminates the problem of the poor flatness of the external side wall ofthe metal case 63 in the eleventh embodiment.

Referring to FIG. 21A, the metal case 63 has a recessed portion 63bprovided at the side wall of the metal case 63. The recessed portion 63bhas a tapered surface merging with the insertion hole 63a. The recessedportion 63b has a diameter greater than the diameter of the insertionhole 63a. The solder preform 86 is provided at the predetermined portionof the optical fiber cut-piece 64, and the optical fiber cut-piece 64 isinserted in the mounting board 21 with the solder preform 86 on the sidewall of the metal case 63. The metal case 63 is heated, so that thesolder preform 86 is melted within the tapered portion 63b. It ispossible to prevent the solder in the melted state from being spread outto the external side wall of the metal case 63.

Referring to FIG. 21B, the metal case 63 has a recessed portion 63cprovided at the side wall of the metal case 63, instead of the taperedportion 63b. The recessed portion 63c includes a stepped surface havinga rectangular cross-section. In this embodiment, solder grains 88 areused instead of the solder preform 86, and the solder grains 88 areplaced in the recessed portion 63c. Similarly to the above embodiment ofFIG. 21A, it is possible to prevent the solder in the melted state frombeing spread out to the external side wall of the metal case 63.

In the above twelfth embodiment, the flatness of the external side wallof the metal case 63 can be maintained, and no problem will be causedwhen attaching the insert holder 70 to the metal case 63 as shown inFIG. 13F.

FIGS. 22A, 22B and 22C show a modification of the twelfth embodiment inFIGS. 21A and 21B. As shown in FIG. 22A, before the optical fibercut-piece 64 is inserted in the mounting board 21, the solder preform 86(FIG. 21A) is fixed to the stepped surface of the recessed portion 63c(FIG. 21B). As shown in FIG. 22B, the optical fiber cut-piece 64 isplaced into the V-groove of the mounting board 21 through the hole ofthe solder preform 86. As shown in FIG. 22C, the metal case 63 is heatedto melt the solder preform 86, and the optical fiber cut-piece 64 isfixed to the insertion hole 63a by the soldering. In this embodiment,the fixing of the optical fiber to the metal case and the soldering toenclose the mounting board 21 are carried out at the same time. Thepresent embodiment is advantageous to improve the productivity of theoptical module.

FIG. 23 shows a modification of the above embodiment of FIGS. 22A, 22Band 22C. This embodiment provides a method of fixing the solder preform86 to the tapered portion 63c of the metal case 63. As shown in FIG. 23,the solder preform 86 is placed on the stepped surface of the recessedportion 63c, and the solder preform 86 is hit by using a punch 90 sothat the solder preform 86 is fixed to the recessed portion 63c.

FIGS. 24A, 24B and 24C show a modification of the above embodiment ofFIGS. 22A, 22B and 22C to improve the adhesion and stability of thesoldering.

Referring to FIG. 24A, the recessed portion 63c has a metal platinglayer 91 on the entire surface of the recessed portion 63c. The metalplating layer 91 in this embodiment is deposited on the side wall of themetal case 63 by one of nickel (Ni) plating (2-5 μm thick) and gold (Au)flush plating (0.2 μm thick). A nickel (Ni) plating is deposited on theother surface of the metal case 63 different from the recessed portion63c. By this modification, the spreading of the solder from the recessedportion 63c to the outside of the metal case 63 is safely prevented, andthe adhesion and stability of the soldering is improved.

Referring to FIG. 24B, the recessed portion 63c has a roughed surface 92on the side wall thereof. This roughed surface 92 is formed by a millingcutter. By this modification, the adhesion and stability of thesoldering is improved. As shown in FIG. 24B, the solder preform 86 isplaced on this roughed surface 92 of the recessed portion 63c, and thesolder preform 86 is hit by using the punch 90 (FIG. 23) so that thesolder preform 86 is firmly fixed to the recessed portion 63c.

Referring to FIG. 24C, the recessed portion 63c has a number of grooves93 provided on the side wall of the recessed portion 63c. The grooves 93radially extend from the center of the insertion hole 63a as shown. Bythis modification, the adhesion and stability of the soldering isimproved. In FIG. 24C, the solder preform 86 (not shown) is placed onthe recessed portion 63c, and the solder preform 86 is hit by using thepunch 90 (FIG. 23) so that the solder preform 86 is firmly fixed to therecessed portion 63c.

In the above embodiments of FIGS. 23 through 24C, the metal case 63 hasthe recessed portion 63c (FIG. 21B) with the stepped surface having arectangular cross-section. However, the above embodiments of FIGS. 23through 24C may also be applied to the metal case 63 having the recessedportion 63b (FIG. 21A) with the tapered surface.

FIGS. 25A, 25B and 25C show an optical module in a thirteenth embodimentof the present invention. The present embodiment provides another methodof fixing the optical fiber cut-piece 64 to the metal case 63.

As shown in FIG. 25A, a solder piece 94 is fixed to the predeterminedportion of the optical fiber cut-piece 64. As shown in FIG. 25B, theoptical fiber cut-piece 64 is inserted in the insertion hole at therecessed portion 63c of the metal case 63. As shown in FIG. 25C, theentire metal case 63 is heated so that the solder piece 94 is melted bythe heat. The method of fixing the optical fiber cut-piece 64 in thepresent embodiment allows a reduction of the number of parts needed forthe soldering during the assembly. The previous fixing process to fixthe solder preform 86 to the metal case 63 by using the punch 90 is nolonger needed, and the method of fixing the optical fiber cut-piece 64in this embodiment provides a more simple fixing process.

If the positioning of the solder piece 94 on the optical fiber cut-piece64 in the present embodiment is performed with a high level of accuracy,it is possible to use the solder piece 94 as the stopper to position theoptical fiber cut-piece 64 on the mounting board 21.

FIGS. 26A through 26G show a method of producing the optical module inthe thirteenth embodiment in FIGS. 25A, 25B and 25C. In FIGS. 26Athrough 26G, the parts which are the same as corresponding parts inFIGS. 13A through 13G are designated by the same reference numerals.

In the present embodiment, as shown in FIGS. 26B and 26G, before theoptical fiber cut-piece 64 is inserted in the mounting board 21, theretaining board 69 is mounted on the mounting board 21, and the wirebonding for the electrical connection is performed.

As shown in FIG. 26C, the lid 66 is mounted on the metal case 63, andthe optical fiber cut-piece 64 with the solder piece 94 fixed isinserted in the mounting board 21 through the recessed portion 63c ofthe metal case 63. Since the solder piece 94 serves as the stopper toposition the optical fiber cut-piece 64 on the mounting board 21, thepositioning of the optical fiber cut-piece 64 is performed with a highlevel of accuracy.

As previously described with FIGS. 6A through 7B, the insertion hole 41(or 41A) with a high level of accuracy can be formed by connecting themounting board 21 and the retaining board 69. As previously describedwith FIG. 14, the positioning of the insertion hole 41 of the mountingboard 21 to the insertion hole 63a of the metal case 63 with a highlevel of accuracy can be performed. Therefore, the optical fibercut-piece 64 can easily pass through the insertion hole 63a of the metalcase 63 in the present embodiment.

As previously described with FIGS. 8A and 8B, the glass capillary 43 canbe used instead of the retaining board 69 to form the insertion hole 41Bin the present embodiment.

Other steps of the method of producing the optical module of the presentembodiment are essentially the same as corresponding steps of theproduction method of the sixth embodiment in FIGS. 13A through 13G.

In the above thirteenth embodiment of FIGS. 26A through 26G, the metalcase 63 has the recessed portion 63c (FIG. 21B) with the stepped surfacehaving a rectangular cross-section. However, the above embodiment mayalso be applied to the metal case 63 having the recessed portion 63b(FIG. 21A) with the tapered surface.

FIGS. 27A through 27D show a method of the connection of the opticalfiber using the insert holder 70. The insert holder 70 is as shown inFIGS. 13F and 26F.

Referring to FIGS. 27A through 27D, the insert holder 70 has a lowerbase 70B and an upper retainer 70C. FIG. 27D is a cross-sectional viewof the optical module taken along a line A--A' in FIG. 27C. The glasscapillary 71 is mounted on the lower base 70B and fixed thereto. Asshown in FIG. 27B, after the optical fiber cut-piece 64 is fixed to themetal case 63, the optical fiber cut-piece 64 is inserted into the glasscapillary 71 on the lower base 70B of the insert holder 70.

A core of the optical fiber 30 is inserted into the glass capillary 71.A slit 71a of the glass capillary 71 is filled with the adhesive agentto connect together the optical fiber 30 and the optical fiber cut-piece64.

As shown in FIG. 27C, an adhesive agent 98 is supplied to the peripheryof the glass capillary 71 so that the glass capillary 71 is enclosed bythe adhesive agent 98. This adhesive agent 98 is any type of urethaneresin, polyimide resin and silicon resin. Finally, the glass capillary71 is sealed by the upper retainer 70C.

In the previous embodiments shown in FIGS. 13F and 26F, the adhesiveagent 98 is not shown. It is desirable to use the adhesive agent 98 asin the above embodiment shown in FIG. 27C. The adhesive agent 98 servesto avoid damage or cut-away of the core of the optical fiber 30.

As shown in FIGS. 27A through 27D, the metal case 63 has a recessedportion which is similar to the recessed portion 63b shown in FIG. 21A.

FIG. 28 shows a modification of the optical module in FIG. 27C. As shownin FIG. 28, the optical module includes a heat-shrinkage tube 99 whichconnects the insert holder 70 and the optical fiber 70, in addition tothe construction shown in FIG. 27C.

FIGS. 29A and 29B show an optical module in a fourteenth embodiment ofthe present invention. This embodiment improves the connection of theoptical fibers by using the glass capillary.

Referring to FIG. 29A, the glass capillary 71 (FIGS. 13F, 26F and 27C)is used to connect an optical fiber 30a and the optical fiber cut-piece64. The glass capillary 71 is the same as those shown in FIGS. 13F, 26Fand 27C. The glass capillary 71 includes the slit 71a, and the slit 71ais filled with an adhesive agent 100. The optical fiber cut-piece 64 andthe optical fiber 30a are connected by the adhesive agent 100 includedin the slit 71a, as shown. This adhesive agent 100 serves to match therefraction rates of the optical fibers.

Referring to FIG. 29B, the glass capillary 71 includes slits 101 inaddition to the slit 71a, and the slits 101 are located on both sides ofthe slit 71a. Similarly to that shown in FIG. 29A, the glass capillary71 is used to connect the optical fiber 30a and the optical fibercut-piece 64 in this embodiment. The slit 71a is filled with theadhesive agent 100 so that the optical fibers 30a and 64 are connected,and the slits 101 are filled with an adhesive agent 102. The adhesiveagent 102 serves to reinforce the connection of the optical fibers. Thestrength of the connection of the optical fibers to resist a tensilestress is increased by this adhesive agent 102.

FIG. 30 shows an intermediate structure of the optical module in thepresent embodiment. Referring to FIG. 30, the intermediate structure ofthe optical module includes the glass capillary 71 shown in FIG. 29B. Inthis glass capillary 71, the optical fiber cut-piece 64 is fixed to theglass capillary 71. Instead of the glass capillary 71 in FIG. 27B, thisglass capillary 71 is used in the fourteenth embodiment. Theintermediate structure of this embodiment prevents a misalignment of theoptical fiber cut-piece 64 and the glass capillary 71 on the opticalmodule which may take place during the assembly.

In the intermediate structure shown in FIG. 30, the glass capillary 71and the insert holder 70 are provided on a lower base 70B. The lowerbase 70B protects the optical fiber cut-piece 64 from being harmed ordamaged. Therefore, the intermediate structure of this embodiment isvery effective to prevent damage of the optical fiber cut-piece 64, andthe intermediate structure can easily be handled during the production.

Further, the present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. An optical module comprising:a mounting boardhaving an upper surface and a longitudinal optical axis parallelthereto; an optical element supported on the upper surface of themounting board and having an optical axis aligned with the longitudinaloptical axis; a groove extending longitudinally in the mounting board,centrally thereof and parallel to the optical axis, and having an openend at a first end of the mounting board and a closed end,longitudinally displaced from the first end at an internal positionwithin the mounting board; an optical fiber having an optical axis, theoptical fiber inserted in and supported by the groove in the mountingboard to align the optical axis thereof with the longitudinal opticalaxis, the groove having a vertical stopper surface therein,perpendicular to the longitudinal optical axis and displaced axiallyfrom the closed end of the groove, the vertical stopper surface abuttedby a free, leading end of the optical fiber when inserted therein; and apositioning mark provided on the mounting board and defining a mountingposition of the optical element on the mounting board at which theoptical element, with an optical axis thereof aligned with thelongitudinal optical axis, is displaced by a prescribed longitudinaldistance from a free, leading end of an inserted optical fiber asdetermined by the abutment thereof with the vertical stopper surface,the positioning mark being located adjacent to the closed end of thegroove and at a prescribed distance from the stopper surface.
 2. Theoptical module according to claim 1, wherein the groove further includesa first longitudinal portion, extending from the open end and to thevertical stopper surface, having a first width and a second longitudinalportion, extending from the vertical stopper surface to the closed endof the groove, and having a second width smaller than the first width,the first portion receiving the inserted optical fiber therein and thepositioning mark being located adjacent the closed end of the groove. 3.An optical module as recited in claim 1, wherein the positioning markprojects longitudinally over the closed end of the groove and toward thefree, leading end of the inserted optical fiber.
 4. The optical moduleaccording to claim 3, wherein the groove comprises first and secondspaced longitudinally extending sidewalls and the vertical stoppersurface is defined by a pair of first and second projections, integralwith and respectively extending laterally inwardly from the first andsecond sidewalls, transversely to the optical axis, an outer portion ofthe optical fiber engaging the first and second projections and acentral portion of the optical fiber being exposed, between the firstand second projections, to the optical element supported on the mountingboard.
 5. The optical module according to claim 3, wherein thepositioning mark is supported on a projecting portion of an insulatinglayer formed on the upper surface of the mounting board.
 6. The opticalmodule according to claim 1, further comprising:a cylindrical memberprovided within the groove and fixed to the mounting board, the opticalfiber being inserted into the cylindrical member.
 7. The optical moduleaccording to claim 6, wherein the cylindrical member has an insidediameter which is greater than an outside diameter of the optical fiber.8. An optical module as recited in claim 1, further comprising:aretaining board adapted for assembly with the mounting board on theupper surface thereof and having a second, central longitudinal groovetherein, the central longitudinal groove of the retaining board, whenthe retaining board is assembled on the upper surface of the mountingboard, extending in the direction of and aligned with the optical axisof the optical fiber, the first groove and the second groove being inmating relationship and defining a longitudinal insertion hole throughwhich the optical fiber is inserted.
 9. The optical module according toclaim 8, wherein the mounting board includes first portions and theretaining board includes second portions, the second portions beingconnected to the first portions to position the mounting board and theretaining board with respect to each other.
 10. The optical moduleaccording to claim 9, wherein the first portions are first fittinggrooves and the second portions are second fitting grooves, the firstfitting grooves and the second fitting grooves being associated to formother insertion holes, and the optical module further comprisingcylindrical parts inserted into the other insertion holes.
 11. Theoptical module according to claim 9, wherein the first portions arefitting grooves and the second portions are fitting projections, thefitting grooves receiving the fitting projections and therebypositioning and interconnecting the mounting board and the retainingboard with respect to each other.
 12. The optical module according toclaim 1, further comprising:a case in which the mounting board issupported and sealed, the case including a base on which the mountingboard is supported and fixed, sidewalls surrounding the base includingan end sidewall having an insertion hole extending therethrough andaligned with the longitudinal groove and through which the optical fiberis axially inserted, the case having a lid affixed to top edges of thesidewalls and sealing the mounting board therein and the insertion holebeing filled with a solder to fix the optical fiber to the case.
 13. Theoptical module according to claim 12, wherein the base of the case has alateral width with respect to a direction perpendicular to the opticalaxis, the lateral width of the base being the same as a lateral width ofthe mounting board.
 14. The optical module according to claim 12,wherein at least one of the base of the case and a bottom of themounting board in contact with the base includes one of an array ofprojections and an array of recesses formed on the at least one of thebase of the case and the bottom of the mounting board.
 15. The opticalmodule according to claim 12, wherein the optical fiber has a protectioncoating surrounding an axial portion of the optical fiber, which axialportion is disposed within the insertion hole, and a metal platingformed on the protection coating and joined to the sidewall surroundingthe insertion hole.
 16. The optical module according to claim 12,wherein a first portion of the groove, extending longitudinally from thefirst, open end thereof, has an inwardly tapered configuration definedby a taper angle of 53.14° or less.
 17. The optical module according toclaim 12, wherein a center of the insertion hole of the case is locatedabove a center of the optical fiber when the optical fiber is enclosedby the groove of the mounting board.
 18. The optical module according toclaim 12, wherein the mounting board is displaced longitudinally fromthe end sidewall of the case in which the insertion hole is provided.19. The optical module according to claim 12, wherein the case has arecessed portion located adjacent to the insertion hole, the recessedportion being filled with solder affixing the optical fiber to the case.20. The optical module according to claim 19, wherein the recessedportion has a tapered surface merging with the insertion hole.
 21. Theoptical module according to claim 19, wherein the recessed portion has astepped surface having a rectangular cross-section.
 22. The opticalmodule according to claim 19, wherein the solder is provided in therecessed portion of the case before the optical fiber is inserted incase.
 23. The optical module according to claim 19, wherein the solderis provided at a predetermined position of the optical fiber before theoptical fiber is inserted in the case.
 24. The optical module accordingto claim 19, wherein the recessed portion has a metal plating layer. 25.The optical module according to claim 19, wherein the recessed portionhas a roughened surface.
 26. The optical module according to claim 19,wherein the recessed portion has plural grooves therein radiallyextending from a center of the insertion hole.
 27. The optical moduleaccording to claim 12, further comprising:a holder connected to a sidewall of the case at which the insertion hole is provided, the opticalfiber being supported by the holder.
 28. The optical module according toclaim 27, wherein the holder has a glass capillary therein providing anoptical connection between the optical fiber, inserted in the groove ofthe mounting board, to an external optical fiber.
 29. The optical moduleaccording to claim 27, wherein the holder has an adhesive agent thereinaffixing the optical fiber thereto.
 30. The optical module according toclaim 28, wherein the glass capillary has a plurality of slits extendingthrough a sidewall thereof and into which an adhesive agent is infected,the injected adhesive agent affixing the optical fiber to the glasscapillary.
 31. The optical module according to claim 1, wherein themounting board comprises a silicon substrate.
 32. The optical moduleaccording to claim 1, further comprising a connector connecting theoptical module to an external device.
 33. The optical module as claimedin claim 1, wherein the positioning mark defines the mounting positionof the optical element in accordance with visually observing a frontedge of the optical element relatively to the positioning mark asilluminated by visible light.
 34. The optical module as claimed in claim1, wherein the mounting board is made of silicon.
 35. The optical moduleas claimed in claim 1, wherein the axial length of the optical fiber isdifferent from the axial length of the groove.
 36. An optical module,comprising:a mounting board having upper and lower surfaces, spacedsidewalls extending longitudinally, first and second opposite end wallsand a longitudinally extending optical axis parallel to the uppersurface; a groove formed in the mounting board, of a first depththerein, extending longitudinally and in a first direction from a first,open end thereof at the first end wall of the mounting board to asecond, closed end thereof at a location intermediate the first andsecond end walls of the mounting board, the groove configured to receiveand support an optical fiber inserted therein with an optical axis ofthe optical fiber aligned with the longitudinal optical axis; a stoppersurface, within the groove and transverse to the optical axis, a freeend of an inserted optical fiber abutting the stopper surface; and apositioning mark supported on the upper surface of the mounting board ata first distance along the longitudinal optical axis from the stoppersurface and at a second distance along the longitudinal optical axisfrom the second, closed end of the groove for positioning an opticalelement on the upper surface of the mounting board and with an opticalaxis thereof aligned with the longitudinal optical axis.
 37. An opticalmodule as recited in claim 36, wherein the positioning mark is supportedon the upper surface of the mounting board at a first distance, in thefirst direction from the stopper surface and at a second distance, inthe first direction, from the closed end of the groove.
 38. An opticalmodule as recited in claim 37, wherein the groove comprises a firstportion of a first width in a lateral direction transverse to thelongitudinal optical axis, extending longitudinally from the first, openend thereof and to the stopper surface and a second width in the lateraldirection, less than the first width, extending longitudinally from thestopper surface to the second, closed end thereof.
 39. An optical moduleas recited in claim 38, wherein the groove comprise a first portion of afirst depth, extending longitudinally from the first open end thereof tothe stopper surface, and a second portion of a second depth, extendinglongitudinally from the stopper surface to the second, closed endthereof.
 40. An optical module as recited in claim 39, furthercomprising a second groove in the mounting board, of the first depth andextending laterally, transversely to and crossing the first groove, andhaving a sidewall adjacent to the second, closed end of the longitudinalgroove, the sidewall of the second groove defining the stopper surface.41. An optical module as recited in claim 40, wherein the second portionof the groove, of the second width, has a bottom surface inclined in thelongitudinal direction from a second depth at the stopper surface, whichis less than the first depth, to the upper surface of the mounting boardat the second, closed end of the groove.
 42. An optical module asrecited in claim 36, wherein the positioning mark is supported on theupper surface of the mounting board at a first distance, in the firstdirection from the stopper surface, and at a second distance, in asecond direction opposite to the first direction, from the closed end ofthe groove.
 43. An optical module as recited in claim 42, wherein thegroove comprises first and second spaced, longitudinally extendingsidewalls and the stopper surface is defined by a pair of first andsecond projections, integral with and extending laterally inwardly fromthe first and second sidewalls, respectively and transversely to theoptical axis, an outer portion of the optical fiber engaging the firstand second projections and a central portion of the optical fiber beingexposed between the first and second projections to an optical elementsupported on the mounting board.
 44. An optical module as recited inclaim 48, wherein the groove comprises a first portion having a firstbottom surface of a first depth, relatively to the upper surface of themounting board, extending longitudinally from the first open end of thegroove to the stopper surface and to and through the first and secondprojections and a second portion, of a varying depth and having asecond, inclined bottom surface extending from the first depth of thefirst bottom surface to the upper surface of the mounting board at thesecond, closed end of the groove.
 45. The optical module as claimed inclaim 36, wherein the positioning mark defines the mounting position ofthe optical element in accordance with visually observing a front edgeof the optical element relatively to the positioning mark as illuminatedby visible light.
 46. The optical module as claimed in claim 36, whereinthe mounting board is made of silicon.
 47. The optical module as claimedin claim 36, wherein the axial length of the optical fiber is differentfrom the axial length of the groove.